Seashell Strength May Help Create New, Stronger Materials

Seashells are surprisingly strong for being made out of the same material as chalk. Now, scientists are taking a closer look at how seashells get their strength from their own biological material.

Calcium carbonate is one of the most important materials on Earth. It crystallizes into chalk, shells and rocks. Animals and people also use calcium carbonate to make biominerals such as pearls, seashells, exoskeletons, or the tiny organs in the ears that maintain balance. These biominerals include proteins or other organic matter in the crystalline matrix to convert the weak calcium carbonate to hard, durable materials.

Scientists have actually been exploring how organisms produce these biominerals in order to determine the basic geochemical principles of how they form. Now, researchers may have done just that.

"This work helps us to sort out how rather weak crystals can form composite materials with remarkable mechanical properties, said Jim De Yoreo, one of the researchers, in a news release. "It also provides us with ideas for trapping carbon dioxide in useful materials to deal with the excess greenhouse gases we're putting in the atmosphere, or for incorporating light-responsive nanoparticles into highly ordered crystalline matrices for solar energy applications."

In this latest study, the researchers created spheres out of organic molecules, call micelles, and added them to calcite, which is a high concentration of calcium carbonate that forms a crystalline mineral; calcite builds up in layers and creates uneven surfaces during growth, like the terraces on a mountainside.

The researchers found that micelles don't randomly land on the flat terraces. Instead, they only stick to the edges of the steps; the edges hole onto the micelles as the calcium carbonate steps closer around them, one after another. The scientists watched as the growing steps squeezed the micelles. As the step closed around the top of the micelle, first a cavity formed and then it disappeared altogether under the surface of the growing crystal.

The micelles are actually compressed like springs as the steps close around them. These compressed springs create strain in the lattice between the micelles, leading to enhanced mechanical strength.

The findings reveal a bit more about the strength of these shells and may help create new materials in the future.